The invention relates to an (especially polyphase, especially biphase) electronic circuit arrangement (especially suitable or especially configured for generating at least two different stimulation currents in medicine) for generating at least two different constant currents, especially of different (antiphase) polarity, at a load resistor, comprising a bridge circuit (especially an H bridge=H bridge circuit) having at least (in the case of an H bridge, precisely) four legs, and switching elements and a bridge branch between the legs, in which the load resistor can be inserted, and a current source which is connected to the legs of the bridge circuit in such a manner that it provides for a current via one of the legs through the bridge branch through a leg, connected to the other end of the bridge branch, in the case of a corresponding switch position, the use of the circuit arrangement for generating such stimulation currents and corresponding procedures and methods.
For the purpose of generating constant currents, feedback-type operational amplifier circuits have usually been used as current source which, due to their operating principle, always needed a certain quiescent current for stabilizing their operating point. Due to the principle involved, this led to an increased power consumption, especially in the case of high open-circuit voltages, even at times at which the output current is zero. In addition, the use of operational amplifiers (OPA) greatly limited the possibility of a low open-circuit voltage since the OPA needs a minimum operating voltage due to the principle involved. FIG. 1 shows a simplified example of such a bipolar current source with OPA. “Load” is here the load resistor, for example tissue, organs or body parts (such as the head) of a patient which are to be stimulated by current flow in the case of a patient stimulation.
Unipolar current sources which have a FET (such as MOS-FET) or transistor as a switching element in the output branch no longer have such a disadvantage.
FIG. 2 shows, in a simplified manner, such a unipolar current source in which “load” is again the load resistor, for example as defined above. The disadvantageous factor is here, among other things, that defined currents are difficult to implement due to the unipolarity.
As a solution to the problems mentioned, a circuit principle for constant current sources for stimulation in the medical field, primarily for supplying pacemakers with current, is shown in Offenlegungschrift US 2010/0324618. This contains an H bridge (for example identified by the reference symbol 330 in FIG. 5 there, or by the reference symbol 160 in FIG. 2 there).
FIG. 3 shows a simplified representation of the circuit shown for this current source.
In this Figure, 1 is a voltage source, 2 is an adjustable centralized constant current source (which could also be arranged at the lower end of the circuit after the combination of the legs with S2 and S4). When the switching elements S1 and S4 are closed, a (for example positive) current i1 (indicated by arrows in FIG. 3) can flow via the load resistor R (e.g. as defined above) interconnected in the bridge branch by applying the voltage while S2 and S3 are open. An alternative (for example negative, antiphase) current i2 (indicated by arrows in FIG. 3) can flow via the load resistor R by switching on S2 and S3, applying an opposite voltage. This H bridge thus allows the advantage of a biphase constant current source (e.g. for stimulation) when using an asymmetric supply voltage since the two connections (polarization) of the load can be simply exchanged by switching the switching elements.
Due to the principle involved, however, this circuit makes high demands on the timing precision of the switches and of the current source in the case of a change of direction of the current, especially when the positive and the negative direction of current are different. In the case of an inaccurate switch-over, a wrong current value may flow from time to time because, e.g., the new current value (current source 2, FIG. 3) is set, but still flows in the wrong direction through the load because the switch-over of the switches has not yet taken place. In addition, the circuits in US 2010/0324618, which is now U.S. Pat. No. 8,155,740 issued on Apr. 10, 2012, are designed rather for relatively low open-circuit voltages due to their orientation for stimulation of pacemakers which need rather low voltages.